This application relates to the art of thermal switches and, more particularly, to thermal switches that use current carrying actuators of shape memory metal. The invention is particularly applicable for use with rechargeable batteries to prevent thermal runaway and will be described with specific reference thereto. However, it will be appreciated that the invention has broader aspects and can be used for other purposes in applications where protection against excessive current and overheating are desired.
Rechargeable batteries have various physical sizes to fit within electrical devices that are powered by the batteries. Thermal switches that protect rechargeable batteries against excessive current and overheating must fit within the same physical battery envelope. The switch must be very small in order to avoid any significant increase in the physical size of the battery, and to avoid any significant reduction in the size or capacity of the electro-chemical cell.
Because of the very small size of such switches and their components, it is difficult to crimp a switch assembly into a battery case without distorting the switch and its components. Such distortion may render the switch inoperative or undesirably change its operational characteristics so that it no longer will perform its intended function. It would be desirable to have a miniature switch assembly that can be crimped into a battery case without distorting the switch assembly or its operational components in a manner that renders the switch inoperative or changes its operating characteristics.